Gas turbines operate at high temperatures that may reach 1.200° C. and more. Accordingly the turbine blades must be capable of withstanding such high temperatures. For prolonging the life of the blades they often contain cooling systems conducting cooling air through the blade.
A gas turbine blade comprises a root, a platform and an airfoil that extends outwardly from the platform, the airfoil comprising a tip, a leading edge and a trailing edge. During operation of a gas turbine high stresses may be generated in some areas of the turbine blade. Particular life limiting areas are found in the airfoil hub region and the trailing edge region at the hub forming a relatively thin wall on the downstream side of the airfoil. Because of its relatively thin structure and high stresses during operation, the trailing edge is highly susceptible to formation of cracks which may lead to failure of the airfoil.
The cooling system contains internal cooling channels which receive air from the compressor of the gas turbine and pass the air through the blade. The cooling channels include multiple flow paths that are designed to maintain the turbine blade at a relatively uniform temperature. However, centrifugal forces and air flow at boundary layers sometimes prevent some areas of the turbine blade from being adequately cooled, resulting in the formation of localized hot spots which can reduce the lifetime of a turbine blade.
A cooling system in the airfoil may include cooling air passages to maximize convection cooling in the airfoil tip and trailing edge, and discharge a portion of the cooling air through cooling holes in the tip and trailing edge of the airfoil. Such turbine blade is known, for instance, from U.S. Pat. No. 4,278,400.